Title

Author

Date of Award

Degree Type

Degree Name

Master of Engineering Science

School

School of Engineering

Faculty

Faculty of Health, Engineering and Science

First Advisor

Associate Professor Sanjay Kumar Shukla

Second Advisor

Dr Alireza Mohyeddin

Abstract

There are several improvement methods available for modifying soils. Cement stabilisation has been one of the popular improvement methods for cohesionless soils. Over the past three decades, many studies have been done to investigate the effects of adding synthetic and natural fibres to soil as the reinforcing material alone or with cement. Utilisation of the fibres from waste materials such as used tyres and carpets, which are available in large quantities worldwide, can be beneficial.

Though significant research has been conducted on studying the behaviour of cement-stabilised soil, the effectiveness of using waste tyre fibres (TF) with cement has received very limited attention. Therefore, the present work focuses on investigating the characteristics of local Perth sandy soil after inclusion of waste TF and cement. These wastes can be utilised in ground improvement in large quantities and could provide a cost-effective and environmentally friendly strategy that avoids tyre disposal problems.

A series of laboratory tests including compaction, unconfined compression and triaxial tests were conducted to investigate the effects of adding TF and cement on the engineering behaviour of Perth sandy soil. Two types of TF namely tyre fibres A (TFA) whose particles were smaller in length and diameter than the other type called tyre fibres B (TFB) were used. The contents were varied from 0 to 3% of dried sand by weight both for cement and TF. The cemented specimens were cured in a humid room for 7 days. For the triaxial tests, the confining stresses were 50, 100 and 200 kPa.

The compaction test results indicate that the maximum dry unit weight is generally increased by adding cement and decreased by TF inclusion, while adding cement and TF results in a lower optimum water content.

The results of unconfined compression tests show that the cement addition increases the unconfined compressive strength (UCS ) of the sand and sand-TF mixtures. Furthermore, the inclusion of TF in the sand increases its UCS , whereas UCS of the sand-cement mixtures decreases with an increase in tyre fibre content, except for a slight increase at low cement contents. The highest improvement occurred when 1% TFB was added to sand + 1% cement with an increase of UCS from about 314 kPa to 338 kPa. Moreover, while adding the cement increases the modulus of elasticity ( E ), the inclusion of TFs reduces E , and the greatest reduction was observed when 3% TFB was added to sand with 3% cement ( E decreased from about 4186 kPa to 1537 kPa).

The triaxial results indicate that adding TF to sand leads to a slightly higher effective angle of friction with a reduced effective cohesion. However, overall, a marginal difference is observed in the stress-strain characteristics of unreinforced and TF-reinforced soil. Generally, it was observed that the use of TFB was slightly more efficient compared to TFA in both cemented and uncemented sand mixtures due to higher aspect ratios of TBF and accordingly, greater reinforcement effect. Overall, TF-reinforced sand, with or without cement, is a lighter material with improved strength, which can be used in some civil applications such as slope stabilisation, backfills or embankments.

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